This invention relates to production of broad heat sealable OPP film with excellent heat sealability and surface properties and to a method of making same.
In certain types of packaging, for example, foods such as cookies and the like, it is common to employ a multilayer film having two or more polymeric layers wherein one of the layers is known to be an effective heat seal layer. In the packaging process a supply of such a multilayer film can be shaped into a tube in a vertical and horizontal form, fill and seal machine. Marginal regions of heat seal layer are brought into face to face relationship and heat sealed together. Thereafter the packaging machine automatically forms a heat seal and makes a horizontal severence across the bottom of the bag; the product is dispensed into the open end of the tube and thereafter a second horizontal seal is effective across the tube with a simultaneous severing through the tube to result in a product packaged in a tube, heat sealed at both ends and along one seam at right angles to the end seals. While the food or other product is being dispensed into the package air is also present in the package and thus air assists in protecting and cushioning a product during subsequent shipment of the finished packages.
A multilayered wrapping film described in U.S. Pat. No. 4,214,039 discloses a film structure comprising a polyethylene film substrate having a heat sealable vinylidene chloride polymer, in between the polypropylene film and the vinylidene chloride polymer is a primer coat which enhances the bond strength between the polypropylene and the heat sealable vinylidene chloride polymer. This packaging is effective for comparatively small quantities of product. For packaging of comparatively large quantities its seal strength needs to be increased.
U.S. Pat. No. 4,564,558 is directed to an oriented multilayered heat sealable film structure of greater strength comprising a polyolefin film substrate, a layer of a terpolymer of ethylene, propylene and butene, a prime layer on said terpolymer layer and a heat sealable layer on said primer layer.
The packaging industry has been moving toward higher productivity requiringa broad heat sealable film. Also required in the field application is an excellent film surface for lamination and printing processes. This invention, therefore, relates to broad heat sealable film with excellent surface and barrier properties.